Some of conventional ejectors disclosed in, for example, Patent Document 1 and Patent Document 2 have been known. The ejector of this type includes a nozzle portion that depressurizes a refrigerant condensed and liquefied by a refrigerant condenser after compressed to a high pressure by a compressor when the ejector is used in a refrigeration cycle, a suction portion that draws a lower pressure side refrigerant flowing out of a refrigerant evaporator, and a diffuser portion that mixes the refrigerant ejected from the nozzle portion with the refrigerant drawn from the suction portion and increases a pressure of the mixture.
Further, the nozzle portion of the ejector in Patent Document 1 includes a first nozzle that depressurizes and expands a liquid refrigerant which flows therein from the refrigerant condenser, and a second nozzle that again depressurizes and expands the refrigerant that has been put into two phases of gas-liquid by the first nozzle, and ejects the refrigerant. With the above configuration, the refrigerant is expanded into the two phases of gas-liquid by the first nozzle, and further depressurized and expanded by the second nozzle. As a result, an exit velocity of the refrigerant that flows out of the second nozzle can be increased, and nozzle efficiency can be improved.
In a general ejector, a diffuser portion (pressure increase part) is coaxially disposed on an extension line in an axial direction of a nozzle portion. In addition, Patent Document 2 discloses that a spread angle of the diffuser portion thus arranged is relatively reduced to enable an improvement in the ejector efficiency. The nozzle efficiency means an energy conversion efficiency when a pressure energy of the refrigerant is converted into a kinetic energy in the nozzle portion. The ejector efficiency means an energy conversion efficiency as the overall ejector.
However, in the ejector of Patent Document 1, when a refrigerant pressure difference between a high pressure side and a low pressure side is small, for example, when a load of the refrigeration cycle is low, most of the refrigerant pressure difference is depressurized by the first nozzle, and the refrigerant can be hardly depressurized in the second nozzle. As a result, in the low load of the refrigeration cycle, there arises such a problem that the refrigerant may not be sufficiently pressurized in the diffuser portion. In other words, in the ejector of Patent Document 1, the sufficient operation of the ejector which is commensurate with the load of the refrigeration cycle may not be obtained.
On the contrary, the following configuration is proposed. The diffuser portion having the relatively small spread angle disclosed in Patent Document 2 may be applied to the ejector of Patent Document 1, to thereby improve the ejector efficiency and pressurize the refrigerant sufficiently in the diffuser portion even in the low load of the refrigeration cycle.
However, when the diffuser portion disclosed in Patent Document 2 is applied to the ejector in Patent Document 1, a length of the nozzle portion in the axial direction becomes longer, and a body size of the ejector becomes unnecessarily larger in the normal load of the refrigeration cycle.
In the ejector of Patent Document 1, because each nozzle is configured by a fixed throttle, a flow rate of the refrigerant cannot be adjusted, and the ejector cannot be operated in correspondence with a load variation of the refrigeration cycle.
On the contrary, it is conceivable to add an adjustment mechanism for adjusting a throttle opening (flow channel area) of a throttle passage (nozzle passage) that depressurizes and expands a high-pressure refrigerant according to a temperature and a pressure of an evaporator outflow refrigerant such as a temperature type expansion valve.
The above adjustment mechanism includes a valve body for adjusting the throttle opening, a diaphragm that is displaced according to a difference between an internal pressure in a sealed space in which a temperature sensitive medium varied in pressure according to a temperature of the evaporator outflow refrigerant is sealed and the pressure of the evaporator outflow refrigerant, and an actuating bar for transmitting a displacement of the diaphragm.
However, a general thermal expansion valve is of a structure in which the actuating bar and the valve body are housed in a body configuring a shell of the thermal expansion valve, the sealed space and the diaphragm are disposed outside of the body, and a temperature of the temperature sensitive medium is likely to be affected by an external ambient temperature. When the temperature of the temperature sensitive medium is affected by the external ambient temperature, the valve body may be displaced regardless of the temperature of the evaporator outflow refrigerant, and the operation of the refrigeration cycle may become unstable.
For that reason, even if the adjustment mechanism employed in the thermal expansion valve is applied to the ejector, it is difficult to adjust the refrigerant flow rate according to the temperature and the pressure of the evaporator outflow refrigerant, which still makes it difficult to obtain the sufficient operation of the ejector commensurate with the load of the refrigeration cycle.